brake question

[backinblack]

First off, you people are GREAT!! Wouldn't dream of restoring this truck without you........

I am working on a 69 LWB four wheel drum brake truck with no power assist.

My pedal keeps going almost to the floor, unless pumped like crazy.

The master cylinder is still full of brake fluid, and maintains levels, so, I thought this would eliminate possibility of wheel cylinders being the culprit.

Any ideas where I could start to get some pedal back?

TIA!

[stllookn]

It sounds like seals on your master cylinder are shot. I would replace the master cylinder, they are pretty inexpensive...like $15 at CSK. I would also consider rebuilding the wheel cylinders and checking all the brake lines and hoses too as well as replacing all the brake fluid. It is no fun losing the brakes. Just my 0.02.

[VetteVet]

Brake shoes are worn down. If you have the freeplay set correctly and the pedal goes to the floor but will pump up solid this is the usual problem. At first I thought it might be the master cylinder bypassing or air in the line, but if the brakes are not spongy you probably just need to adjust the shoes or replace them if they are worn too badly.

[thecatseye66]

I just went through this with my 68 c-20, but I have a power booster on mine (I don't think it matters though). I'm picky as hell with brakes 'cause I let my girlfriend haul her horses with this truck. Four wheel drums are pretty archaic--I tell everyone it has ABS (archaic braking system).

The cause of mine was severely corroded wheel cylinders in the front.

The PO had put on a new MC thinking that was the culprit, but after numerous bleeding attempts they still had a lot of travel at the pedal and when they hooked up it locked the brakes into a skid. When I got the truck home I tore off the hubs and sure enough, those wheel cylinders were leaking a little bit, but not enough to make the fluid loss really noticeable. I priced out the front wheel cylinders locally for about 50 bucks a pop (chevyduty and others carry them cheaper but the shipping costs makes it close to that). The front cylinders are NOT the same as the back on C-20's--if you have a C-10 they might be cheaper. The rebuild kits were $3.50 each.

I rebuilt the original wheel cylinders and now the brakes work great. I didn't even change the shoes because they had about a solid 3/8 left.

I think once a wheel cylinder begins to corrode internally it just doesn't have the travel and rebound capabilities that it should have. the inner walls of the cylinder and the piston cups get full of a mixture of rust and grease and just makes the whole mechanism gummy and sticky. Add that to a loss in brake fluid pressure (even a small leak will drop pressure to the shoes) and you can have some very unresponsive brakes.

I've heard you shouldn't hone a wheel cylinder any more than .02 thousandths so be careful if you rebuild them. Most of the corrosion occurs at the center of the cylinder, below the line inlet and bleeder. Mine actually had pitting in those areas but the sides of the cylinder where the cups ride back and forth was still good with no corrosion. Knock out the crap with a brake fluid soaked hone and don't worry too much about the black stains in the cylinder wall--those are from the cups wearing down and they won't hurt the functionality at all.

[backinblack]

Ok....I'm looking to check the shoes, but how do these drums come off? Do I have to pull the dust cover ,and cotter pin, etc, or what? There's so much crap on em I can't tell for sure. And what's the big spring all the way around the drum?

[thecatseye66]

Originally Posted by backinblack

Ok....I'm looking to check the shoes, but how do these drums come off? Do I have to pull the dust cover ,and cotter pin, etc, or what? There's so much crap on em I can't tell for sure. And what's the big spring all the way around the drum?

backinblack,
It's not that bad, that spring stays on the drum--I'm not completely sure of its function but I've heard it has to do with noise suppression. There is a spring inside the dust cover too which I've been told was for noise suppression as well--

just twist the dust cover off with a pair of channellocks, remove the cotter pin and the wheel bearing retaining nut and washer and the hub should come without too much hassle.

Here's decent link to a website with a lot of pictures. Some guy put this together when he rebuilt the REAR drums on his truck. The front brakes are much simpler and have less components (no axle to pull, no e-brake cable connector) but the pictures and the process of rebuilding are nearly identical.

http://www.lighthouse57.com/brakes.htm

A word of advice: only tear down and work on one side at a time so you have a reference to look at when you put them back together.

[backinblack]

Thanks!!

[68haywagon]

If your gonna put new shoes on do yourself a favor while you are in there and replace the wheel cylinders, hoses, springs, front bearings, and cut the drums. Unless you knew the PO or had the work done before while you owned it god only knows how old the stuff is. It's really not that expensive to know the brakes will work. I replaced everything on mine including the brakes lines and wow what a difference. It wasn't that hard to do if you take your time and only do one side at a time. I did my whole brake system without the new SS lines for like $150-175.

Good luck,
Mike

[briarpatch]

My brakes were doing the same thing and it was the master cylinder. I did have the advantage of knowing that all the other brake system components were ok, as I had a complete brake job done 15k miles ago. And yes, MS are cheap. I paid $14.99 for one!